variable edge weight

src/qiskit_qec/decoders/hdrg_decoders.py

@@ -22,6 +22,7 @@
 from typing import Dict, List, Set, Tuple
 
 from rustworkx import PyGraph, connected_components, distance_matrix
+import numpy as np
 
 from qiskit_qec.decoders.decoding_graph import DecodingGraph
 from qiskit_qec.utils import DecodingGraphEdge
@@ -291,7 +292,11 @@ class UnionFindDecoder(ClusteringDecoder):
     by the peeling decoder for compatible codes or by the standard HDRG
     method in general.
 
-    See arXiv:1709.06218v3 for more details.
+    To avoid using the peeling decoder, and instead use the standard
+    method for clustering decoders to get corrections, set `use_peeling=False`.
+    Growth unit is 0.5 by default, but can be changed with `growth_unit`.
+    To use half the minimum boundarye edge weight for each clustering round,
+    set `growth_unit=None`.
     """
 
     def __init__(
@@ -300,6 +305,7 @@ def __init__(
         decoding_graph: DecodingGraph = None,
         use_peeling=True,
         use_is_cluster_neutral=False,
+        growth_unit=0.5,
     ) -> None:
         super().__init__(code, decoding_graph=deepcopy(decoding_graph))
         self.graph = self.decoding_graph.graph
@@ -308,6 +314,8 @@ def __init__(
         self.use_peeling = use_peeling
         self.use_is_cluster_neutral = use_is_cluster_neutral
         self._clusters4peeling = []
+        self.growth_unit = growth_unit
+        self._growth_unit = None
 
     def process(self, string: str, predecoder=None):
         """
@@ -463,10 +471,20 @@ def _grow_clusters(self) -> List[FusionEntry]:
             clusters that will be merged in the next step.
         """
         fusion_edge_list: List[FusionEntry] = []
+
+        if self.growth_unit:
+            self._growth_unit = self.growth_unit
+        else:
+            min_weight = np.inf
+            for root in self.odd_cluster_roots:
+                cluster = self.clusters[root]
+                for edge in cluster.boundary:
+                    min_weight = max(min(min_weight, edge.data.weight), 0)
+            self._growth_unit = min_weight / 2
         for root in self.odd_cluster_roots:
             cluster = self.clusters[root]
             for edge in cluster.boundary:
-                edge.data.properties["growth"] += 0.5
+                edge.data.properties["growth"] += self._growth_unit
                 if (
                     edge.data.properties["growth"] >= edge.data.weight
                     and not edge.data.properties["fully_grown"]
@@ -546,22 +564,27 @@ def _merge_clusters(self, fusion_edge_list: List[FusionEntry]):
 
             # see if the cluster is neutral and update odd_cluster_roots accordingly
             fully_neutral = False
-            for nodes in [
-                [self.graph[node] for node in cluster.atypical_nodes],
-                [
-                    self.graph[node]
-                    for node in cluster.atypical_nodes
-                    | (set(list(cluster.boundary_nodes)[:1]) if cluster.boundary_nodes else set())
-                ],
-            ]:
-                if self.use_is_cluster_neutral:
-                    fully_neutral = self.code.is_cluster_neutral(nodes)
-                else:
-                    neutral, extras, num = self.code.check_nodes(nodes)
-                    for node in extras:
-                        neutral = neutral and (not node.is_boundary)
-                    neutral = neutral and num <= len(cluster.edge_support)
-                    fully_neutral = fully_neutral or neutral
+            if self._growth_unit:  # assume non-neutral while growing along 0-weight edges
+                for nodes in [
+                    [self.graph[node] for node in cluster.atypical_nodes],
+                    [
+                        self.graph[node]
+                        for node in cluster.atypical_nodes
+                        | (
+                            set(list(cluster.boundary_nodes)[:1])
+                            if cluster.boundary_nodes
+                            else set()
+                        )
+                    ],
+                ]:
+                    if self.use_is_cluster_neutral:
+                        fully_neutral = self.code.is_cluster_neutral(nodes)
+                    else:
+                        neutral, extras, num = self.code.check_nodes(nodes)
+                        for node in extras:
+                            neutral = neutral and (not node.is_boundary)
+                        neutral = neutral and num <= len(cluster.edge_support)
+                        fully_neutral = fully_neutral or neutral
             if fully_neutral:
                 if new_root in self.odd_cluster_roots:
                     self.odd_cluster_roots.remove(new_root)